Field of the Invention
The present invention is generally directed toward polymeric nanocomposite materials comprising polycyclic aromatic hydrocarbon groups directly incorporated into a polymer network along with free polycyclic aromatic hydrocarbon compounds dispersed within the polymer matrix. In particular, the polycyclic aromatic hydrocarbon compounds improve the thermal, rheological, and physical properties of the resulting nanocomposites.
Description of the Prior Art
In many rigorous applications for polymeric materials, especially those involving thermoset resins, where there is a desire to modify or change the material to potentially improve it's thermal, rheological, and physical performance, but where modifications or changes to the material are highly undesirable for a variety of reasons, including the material having known and well behaved aging and compatibility characteristics, it may be desirable to be able to make small changes to the material that result in large changes in the material's key properties. One such key property is a polymeric material's glass transition temperature (Tg).
The Tg, perhaps more than any other property, dictates the temperature above or below which a polymeric material can be used reliably. For example, polystyrene, which is used in the manufacture of foam coffee cups, has a Tg of about 100° C. Above 100° C., above polystyrene's Tg, it becomes viscous, flexible, and easily distorted. Thus, polystyrene foam is best suited for use below its Tg. Polybutadiene, an elastomer that is used in automobile tires, however, is an example of a polymer that is often utilized at conditions above its Tg. Polybutadiene has a Tg of about −103° C. Below this temperature, it is a hard, rigid, inflexible solid.
By changing the Tg of a polymer, it can be made suitable for new applications, or for known applications with different thermal, rheological, and physical requirements. Most often, changing the Tg for a particular polymer may be accomplished through the use of additives that are mixed with the polymer material. Lowering the Tg for a particular polymer may be accomplished, for example, through the use of plasticizers. The addition of fillers can often result in increased Tg values. The use of nanoparticle fillers has been proposed for this purpose, including clay, silica, and carbon black. Nanofillers like these do not consist of discrete molecules, which may be agglomerated or crystallized on the nanoscale, but are rather particles. The effects of the nanoparticle based nanofillers on Tg can be highly material specific and somewhat unpredictable. Scientifically and commercially important molecular nanofillers include Fullerene (C60), and polyhedral oligomeric silsesquioxane (POSS), among many others. However, polycyclic aromatic hydrocarbons are also capable of behaving like molecular nanofillers. When applied properly small amounts of polycyclic aromatic hydrocarbons can significantly improve the thermal, rheological, and physical properties of the resulting polymeric nanocomposites, including significant increases in its Tg.